Olefin feed purification in an alkylation process

ABSTRACT

An olefin stream, e.g., ethylene, produced, for example, by naphtha cracking and containing methane and hydrogen impurities is absorbed from the major portion of the impurities using a portion of the subsequently produced alkylate. Alkylate containing absorbed ethylene is flashed, the liquid remaining after flashing is passed to a fractionation column from which an isoparaffin such as isobutane is removed and admixed with flashed vaporous ethylene, and the mixture is charged as feed to an alkylation process.

United States Patent 91 Henderson Mar. 27, 1973 [5 OLEFIN FEED PURIFICATION IN AN Primary Examiner-Delbert E. Gantz ALKYLATIO N PROCESS Assistant ExaminerG. J. Crasanakis [75] Inventor: Miles L. Henderson, Bartlesville, Attorney-Young and Qmgg Okla. C B [57] ABSTRACT 73 Assi nee: Philli s Petroleum om an ar- 1 g fi 0k]a p y, An olefin stream, e.g., ethylene, produced, for exam ple, by naphtha cracking and containing methane and [22] Filed: Aug. 1 9, 1971 hydrogen impurities is absorbed from the major por- [21] APPL No; 173,069 tion of the impurities using a portion of the subsequently produced alkylate. Alkylate containing absorbed ethylene is flashed, the liquid remaining after flashing is passed to a fractionation column from n which an lsoparaffin such as lsobutane is removed and [58] gk g rg admixed with flashed vaporous ethylene, and the mixture is charged as feed to an alkylation process.

5 Claims 1 Drawi F re [56] References Cited UNITED STATES PATENTS 286,504 6/1942 Parker ..260/68'3.6l

FUEL GAS I2 38 5 35 E '6 19 n: 42 (/0) r 29. 12 a; m E

l0 Q Q E, 43 Z I3 E T Z 28 g I E P 37 E 2 W VALKYLATION r3 4| 'W AND E E T ZONE 30mm g 2 1 LL L, C4 c Fuzo I7 32 Z: LC4 AND HEAVIER 24 94 ALKYLATE FUEL GAS Pmnmnmznm c AND LIGHTER FEED GA M. L. HENDERSON This invention relates to the separation and conversion of hydrocarbons. In accordance with one aspect, this invention relates to a purification and conversion process wherein olefin feeds comprising ethylene containing lower boiling impurities are freed of the impurities using a portion of subsequently produced product from the .purified olefin stream, In accordance with another aspect, ethylene produced, for example, by naphtha cracking and containing methane and hydrogen impurities is absorbed from a major portion of the impurities using a portion of subsequently produced alkylate as the absorbent. In accordance with another aspect, an absorbent comprising alkylate and absorbed ethylene is flashed to separate an ethylenerich vapor which is combined with a liquid isoparaffin such as isobutane and the mixture is utilized as the feed for an alkylation process to produce alkylate which is subsequently used in part as the absorbent to recover ethylene from an olefin-containing stream. In accordance with a' further aspect, this invention relates to a process for the production of DIP alkylate wherein at least a portion of the DIP alkylate product is used to absorb ethylene from an olefin-containing stream containing lower boiling impurities and the absorbed ethylene is separated'from the absorbent and used as the olefin feed for the DIP alkylation.

Processes for the alkylation of hydrocarbons, for example, alkylation of isobutane with ethylene to produce diisopropyl, by means of catalysts such as aluminum chloride-hydrocarbon complex are well known to the art. Also as well known to the art, it is desirable to operate the DIP alkylation unit with high purity ethylene feed.

In accordance with the invention, it has been found that ethylene streams containing low boiling impurities can be substantially freed of theseimpurities by contacting with a DIP alkylate, as absorption liquid (or absorbent), under absorption conditions.

Accordingly, an object of this invention is to provide an improved purification system for olefin streams.

Another object of this invention is to provide an improved process for the alkylation of isoparaffins with olefins.

A further object of this invention is to provide an improved and economical process for the purification of alkylation olefin feeds.

Other aspects, objects and the several advantages of the invention will be apparent to those skilled in the art upon reading the specification, the drawing and the appended claims,

In accordance with the invention, olefin streams comprising ethylene and containing low boiling impurities are subjected to absorption by contact with an alkylate product to selectively absorb ethylene from the impurities. The ethylene can be separated from the alkylate absorbent for use as a source of olefin in an alkylation process.

More specifically, in accordance with the invention, ethylene produced, for example, by naphtha cracking and containing methane and hydrogen impurities is absorbed from the major portion of the impurities using a portion of subsequently produced diisopropyl alkylate.

In accordance with a further embodiment of the invention, ethylene is absorbed from olefin-containing streams by contact with DIP alkylate product, the ethylene is flashed from the alkylate absorbent and passed to a DIP alkylation together with an isoparaffin such as isobutane. The liquid remaining after flushing the ethylene from the DIP alkylate absorbent is passed to a fractionation column and isobutane is recovered therefrom and combined .with the flashed ethylene vapors and passed together' to the DIP alkylation process.

A better understanding of the invention will be obtained by reference to the accompanying drawing which diagrammatically illustrates the absorption of ethylene from an olefin-containing stream by contact with a portion of the DIP alkylate in combination with the alkylation of ethylene and isobutane to form DIP alkylate.

Referring now to the drawing, an olefin-containing feed comprising ethylene and lighter materials such as methane and hydrogen is introduced into absorption zone 11 by way of line 10. As is illustrated in the drawing, the olefin-containing feed material is introduced near the'base of absorption column 11 and absorbent comprising DIP alkylate is introduced near the top of absorption column 11 by way of line 12. DIP alkylate absorbent passes downwardly countercurrent to rising olefin-containing material and the ethylene is selectively absorbed by the alkylate and removed together as rich alkylate absorption liquid from the base of absorption column 11 by way of line 13. The lower boiling impurities comprising hydrogen and methane are removed overhead from absorption column 11 by way of line 14 and can be passed for further use, e.g., as fuel.

The ethylene-rich alkylate stream removed by line 13 from the base of absorption column 11 is passed to flash tank 15 wherein the ethylene is flashed overhead and removed by way of line 16. The liquid remaining is removed from tank 15 by way of line 17 and passed to an upper portion of fractionation zone 18.

Fractionation zone 18 is operated under conditions such that isobutane and lower boiling materials are removed overhead by way of line 19, cooled by condenser 35, passed to accumulator 36, and a portion of the liquid isobutane containing stream removed from accumulator 36 by valved line 37 is combined with vaporous ethylene in line 16 and the mixture thus formed comprising isobutane and ethylene is passed by way of line 20 as feed to DIP alkylation zone 21. Some of the liquid removed from accumulator 36 is passed by line 43 to zone 18 as reflux. Makeup or feed isobutane is introduced into zone 21 by way of line 22. Normal butane vapor is removed from a lower portion of zone 18 by way of line 23 and liquid alkylate product is removed from the base of zone 18 by way of line 24. If desired, line 23 can be omitted and normal butane and alkylate can be removed as liquid via line 25 as the absorption liquid, and via line 24 as bottom product, which is charged to a debutanizer, not shown.

In accordance with the invention, a portion of thealkylate product removed from the baseof zone 18 is passed by way of line 25 through pump 26, cooler 27, and thence through line 12 for introduction as absorption liquid into the upper portion of absorption column 11.

The alkylation conditions of temperature, pressure, and ratio of reactants in zone 21 are well known, but these will ordinarily be: temperature, l20F; pressure, 400 psig', hydrocarbon to catalyst volume ratio, lzl; isobutane to ethylene mole ratio, l:l; and the catalyst is an aluminum chloride-hydrocarbon complex in a conventional diisopropyl alkylate manufacturing operation.

In alkylation zone 21 the isobutane and the ethylene are contacted with a suitable catalyst such as aluminum chloride or aluminum chloride complex or other known catalyst under alkylation conditions in liquid phase to produce diisopropyl alkylate. The alkylate, together with propane, normal butane, and unreacted hydrocarbon, is removed from zone 21 by way of line 28 and passed in part to depropanizer column 29. The

remainder of the alkylation effluent is passed by way of line 30 to fractionation zone 18 and introduced into line 17 together with the liquid removed from flash tank and the mixture thus formed isintroduced into zone 18. The:amount'of alkylation effluent passed to zone-29 is sufficient to rid the system of propane and lighter buildup. Alkylation zone 21 includes conventional catalyst separation and recycle means, not illustrated.

Depropanizer column 29 is operated under conditions of temperature and pressure such that propane and lighter materialsare removed overhead by way of line 31, cooled by condenser 38, passed to accumulator 39', and a yield portion is passed by line 41' for further use as desiredLSome of the liquid removed from accumulator 39 vis passed by line 42 to zone 29 as reflux. Heavier materials comprising isobutane 'and'heavier and removed as bottoms from column 29 by way ofline 32 and returned to fractionation zone 18, and is introduced into an upper portion thereof for further separation thereof.

Typical operating conditions for the various zones described above are as follows:

An alkylation process is carried out in accordance with the flow described above in connection with the drawing. An ethylene feed is freed of methane and hydrogen by absorption with a DlP alkylate product produced from the purified ethylene and isobutane. The conditions employed for the various zones are set forth above. 7

The flow rates and compositions of the various streams are set forth below:

Flow Rates:

Vapor Feed to Absorber 701,700 Stream l0), lbs/pay Composition Mol Hydrogen l6 Methane 39 Ethylene 36 Ethane 8 Proprylene (plus) 1 Lean Absorption Oil (Alkylate) 7,300 (Stream l2), BblsJpay Fuel Gas (Stream l4), Lbs/Day 208,000 Composition Mol% Hydrogen 33 Methane 58 Remainder 9 Flashed Vapors (Stream l6), Lbs/Day 227,660 Composition Mol% Hydrogen 3 Methane 3O Ethylene 50 Ethane l2 Heavier 5 "Flashed" Liquid to Fraetionator 9,550 (Stream 1?), BblsJDay Feeds to AICI, Complex Alkylation:

From Fractionator (Stream 37),

Bbls./Day 35,983 Composition Mol% Hydrogen Trace Methane L4 Ethylene 5,6

Ethane 1,4

Propylene Trace Propane 3.3

lsobutane 85.]

Normal butane 3.2

Fresh lsobutane (Stream 22),

Bbls./Day 3,720 (1rVol.% lC,)

Catalyst to Hydrocarbon Vol. Ratio 1:1

lsobutane to Olefin Mol Ratio l0:l

Propane and Lighter (Stream 4i LbsJDay 222,450 (9 Vol. Propane) DIP Alkylate (includes nC,),

(Stream 24), BblsJDay 4.430 DIP Alkylate (C, free), Bbls./Day 4,200 RON, Clear, 102

The absorption zone 11 in the specific example has eight (theoretical) trays. The range of mole ratios of alkylate to ethylene will range from about 0.7 to about 15.

The alkylation reaction can be effected in the following ranges: temperature, to F.; pressure, 275 to 500 psig; hydrocarbon to catalyst volume ratio, 0.521 to 1.5:1; and isobutane to ethylene mole ratio of about 4:1toaboutl3zl.

The invention uses produced alkylate or alkylate containing normal butane as the liquid absorption material 12 for removal of ethylene from gases comprising ethylene, methane, and hydrogen, and effects removal of about 95 percent of the hydrogen and about 75 percent of the methane, with a minimum loss of ethylene and absorption oil in the off-gas 14. When isobutane is used as the liquid absorption fluid, operating the absorber 1 l at the same conditions, a considerable quantity of valuable isobutane is lost overhead with the off-gas 14.

By the removal of the light inert gases 14 from ethylene, the flashed vapor 16 from flash zone can easily be dissolved into the overhead accumulator liquid 37 from tower 18. This overhead vapor 19 can now easily be condensed to liquidusing plant cooling water as the indirect heat exchange fluid in exchanger 35. This allows liquid feed to alkylation which is operated in liquid phase.

The flash step 15 eliminates the requirement for a stripping column for regeneration of ethylene-rich alkylate 13, and the operation is at a lower temperature than used in a rich-oil stripper.

I claim:

1. In an alkylation process wherein an isoparaffin is alkylated with an olefin feed stream in the presence of an alkylation catalyst, the improvement which comprises:

a. purifying said olefin feed stream of lower boiling materials prior to being alkylated by contacting same under absorption conditions with at least a portion of the DIP alkylate recovered from the alkylation process to absorb ethylene from said lower boiling materials, 7 b. flashing ethylene absorbed in step (a) from the DIP alkylate absorbent and passing said ethylene substantially freed of lower boiling materials as the olefin feed stream to the alkylation process for al-.

kylation with an isoparaffln,

e. passing at least a portion of said separated DIP alkylate to step (a) as the absorbent to purify 'said olefln' feed stream.

2. A process according to claim 1 wherein separation in step (d) is effected by passing the alkylation effluent to a depropanizer wherein paraffin and lower materials .are taken overhead and isobutane and heavier materials are removed as bottoms, and said bottoms is passed to a deisobutanizer column wherein isobutane is taken overhead and passed to said alkylation process and DIP alkylate is removed as bottoms.

3. A process according to claim 2 wherein said DIP alkylate absorbent substantially freed of ethylene following flashing is introduced into said deisobutanizer.

4. A process according to claim I wherein said olefin feed stream comprising ethylene is produced by naphtha cracking and contains methane and hydrogen as impurities, and the ethylene is absorbed therefrom by contact with a portion of the subsequently produced DIP alkylate. I

5. A process, according to claim 4 whereinthe ethylene-rich DIP alkylate stream obtained from step a (a) is flashed, the flashed ethylene vapor being taken overhead, and theliquid from the flashing is passed to a deisobutanizer zone from which cooled condensed isobutane is rem'oved overhead andis admixed with the flashed ethylene-rich vapor, and the mixture thus formed is charged as liquid feed to the.alkylation process. 

2. A process according to claim 1 wherein separation in step (d) is effected by passing the alkylation effluent to a depropanizer wherein paraffin and lower materials are taken overhead and isobutane and heavier materials are removed as bottoms, and said bottoms is passed to a deisobutanizer column wherein isobutane is taken overhead and passed to said alkylation process and DIP alkylate is removed as bottoms.
 3. A process according to claim 2 wherein said DIP alkylate absorbent substantially freed of ethylene following flashing is introduced into said deisobutanizer.
 4. A process according to claim 1 wherein said olefin feed stream comprising ethylene is produced by naphtha cracking and coNtains methane and hydrogen as impurities, and the ethylene is absorbed therefrom by contact with a portion of the subsequently produced DIP alkylate.
 5. A process according to claim 4 wherein the ethylene-rich DIP alkylate stream obtained from step (a) is flashed, the flashed ethylene vapor being taken overhead, and the liquid from the flashing is passed to a deisobutanizer zone from which cooled condensed isobutane is removed overhead and is admixed with the flashed ethylene-rich vapor, and the mixture thus formed is charged as liquid feed to the alkylation process. 